Vinyl acetate may be produced by reacting acetic acid, oxygen and ethylene in the presence of a catalyst. The activity of the catalyst may be enhanced by using a promoter such as aqueous potassium acetate. Typically, the reaction is carried out in a fixed bed reactor containing the catalyst. A reactant process stream comprising acetic acid vapour, ethylene and oxygen is fed into the reactor through an inlet. The inlet comprises a pipe having a bend of an angle of between 45 to 90.degree. upstream of the reactor. As reactant molecules flow past the bend in the pipe, they accelerate by varying amounts. This distorts the velocity distribution of the reactant molecules and, as a result, the velocity profile of the process stream is asymmetric.
The catalyst promoter is also introduced into the reactor through the pipe. Conventionally, this is achieved using a spray nozzle which is mounted to an end of a rigid support arm. The support arm is positioned downstream of the bend, and extends perpendicularly into the pipe from the pipe wall. The promoter is introduced into the pipe as liquid droplets from the nozzle; which partially evaporate whilst in the pipe. The promoter is carried by the reactant process stream into the reactor for distribution over the catalyst bed. However, because of the distorted velocity profile of the reactant process stream, the promoter is not deposited evenly over the catalyst. The problem is compounded by the support arm, which, by being configured at right angles to the direction of flow, further distorts the velocity profile of the reactant process stream.